I am working on a modern engine for an old video game, pretty much like those modern engines for Doom game that require the user to provide original Doom game data in order to be runnable.

  • that modern engine requires the user to possess a legal copy of game it emulates
  • that modern engine as it is, does not contain any copyrighted content of games it emulates

I was looking more or less for a license that could cover this case but I didn't find any.

So I decided to write my own license (preliminary but you get the idea):

## Disclaimer

This software as it is offered to the public does not contain coprighted content.

This software is and will always be free for the public, it is made for fun, not for profit.

This software requires legally acquired copies of XXXXX games in order to be usable.

XXXXXX serie of games is the property of XXXXXX.

## License

By using this software you accept the following conditions:

- you CANNOT monetize this free and open source software in any way
- you CANNOT redistribute copies of this software as an executable software
- you CANNOT use illegal copies of copyrighted games needed to build and run this software

If you don't agree with any of these conditions, stop using this software immediately.

We can't be held responsible for inappropriate actions of people on the Internet.

To make it clear, the software will be provided as source code that one will have to build.


Can you suggest which common license, if any, could cover this case ?

Else, what should a custom-written license for this particular case specify ?

(basically, we respect original work but also can't be held responsible for X, Y or Z, etc)

3 Answers 3


Can you suggest which common license, if any, could cover this case ?

No, we can't suggest a license for you, because all the conditions you listed in your draft are restrictions that are not allowed in an open-source license.

Else, what should a custom-written license for this particular case specify ?

A custom-written license should be written by a qualified lawyer. There are just too many details that you would miss or write down in a way that can make the license unenforceable.

For example, the statement This software as it is offered to the public does not contain coprighted content. can be understood to mean that you dedicated our software to the public domain, in which case no license is needed to do whatever you like with the software, including making money with it.

  • Seems like going public domain could be the best thing.
    – aybe
    Commented Apr 27, 2020 at 7:37
  • @Aybe, note that a voluntary public domain dedication is not accepted in all jurisdictions and that public domain effectively means "do what you want. You don't even have to recognize me as the author". Commented Apr 27, 2020 at 10:03
  • Okay, I didn't realize that. Btw, I am sorry, I just realized that I've accepted your answer too quickly as this is something that's quite important, I hope you won't mind.
    – aybe
    Commented Apr 27, 2020 at 16:42

Don't go this way. Solve the problem like many did before you successfully:

Code and assets are two different things. You should be able to clearly distinguish those. Legally you are not allowed to distribute the assets, unless you have written permission by the original distributors or authors of the original game.

Thus the usual solution is to build your game, and use an established open-source license for that. Often a version of GPL is used (OpenTTD, FreeRCT, OpenDune, etc...) to distribute the programme and code. Instructions are commonly provided on how to copy the assets from the original game so that the open source programme can digest it.

This approach also allows to create assets from scratch such that eventually the game finally can be distributed as whole under an open-source license without need for the original assets - while allowing to use the original assets for those who like the original look & feel.

  • Now that really makes things easier, I only need to focus about a licence for the code, thing is, common ones allow commercial uses which sounded like a red flag for me. That's the point I was having a problem with, basically I wanted to tell that it's likely to be illegal to do that. As you can see in the past, even some modding projects for some famous games had to be canceled due to cease and desist.
    – aybe
    Commented Apr 27, 2020 at 16:21
  • A license which does not allow commercial use is not open source so is off-topic here. Commented Apr 28, 2020 at 11:27

Make those restrictions a technical requirement, not a license one

You don't make that a requirement by putting it in the license. You make it a requirement by not shipping any original or replacement assets, since your replacement engine requires these assets to run the game.

Beyond that, it is pointless to put in any extra copy protection, since the original copy protection will likely be completely broken and not even relevant anymore if the game has a modern release (not including remakes or remasters, think GoG) as almost such releases ship with the copy protection removed.

It's pretty pointless to put the requirements in your license anyway; the pirate has already ignored the license of the game developer, what makes you think they'll honour yours?

  • That really makes sense, it's a technical requirement, definitely. And it's not a copy protection at all, since I will support a game that has been released in many regions (USA, Europe, Japan) I need to do a little check about what version the user has inserted so I can read the read the content properly.
    – aybe
    Commented Apr 27, 2020 at 16:09

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